Abstract: Photoplethysmography is a simple technology with low-cost. It can be used to detect blood volume changes in the microvascular. Because the photoplethysmographic devices, which are produced by this technology, are portable and noninvasive, and the data which is received consists of many physiological information of human body, this technology can give great convenience to clinical diagnostic and personal daily health monitoring. This is why it has very broad application prospects. Photoplethysmogram usually consists of an AC component which depends on the blood volume changes in cardiac system, and a DC component which is decided by respiration, tissue, inherent components of blood. Although the origin of the photoplethysmographic signal are being researched still, we can get many valuable information of cardiac system.